This invention relates to blow molding and more particularly to removing parts from blow molding machinery.
Blow molding machines with continuously moving components facilitate high speed, high volume fabrication of hollow articles at low cost. A particular type of blow molding process which can be accommodated in such a system employs pre-molded blanks or preforms at elevated, molding temperature which are remolded to finished form in the high speed machine. In one existing form of continuous system such as described in commonly owned, copending application Ser. No. 415,851, filed Nov. 14, 1973, a plurality of rod assemblies continuously traverse a closed path between successive stations where preforms are first loaded, then blown, then blown articles discharged and finally the assemblies are returned for further loading. Heretofore, whatever was on the rod assembly was ejected at the discharge station -- be it a fully formed, in-specification article or a malformed article -- in order that the continuously moving rod assemblies be available to accept more preforms at the loading station for the next cycle. However, it has been found that not every preform can be expected to be molded into a perfect article. For example, if the preform itself is malformed, or the seal between it and the blow mold for holding blow air is defective, blow pressure during forming cannot be held and the preform may either not blow at all or underblow in the sense of only partially forming the intended article. If the preform is too cold, similar problems occur whereas if it is too hot it may rupture before reaching the wall of the mold cavity during blowing, again presenting a malformed part.
As used herein "underblown part" means either a partially blown or completely unblown molded preform.
Ejecting all parts regardless of quality at the discharge station in the above environment intermingles underblown parts with accurately formed, in-specification articles, which dictates the need for downstream segregation. Deenergizing the continuous system on detection of an underblown part downstream of the blow molds is unattractive, especially if underblown parts frequency is rather high, since the equipment is usually quite substantial in size. Manual clearing of the system without shut down presents a serious safety hazard.